The present invention is directed to golf balls and golf ball-forming microcellular materials, and to methods for forming such golf balls and of controlling material properties and weight distribution of golf balls formed of such materials.
Conventional golf balls can be divided into several general classes: (a) solid golf balls having one or more layers, and (b) wound golf balls. Solid golf balls include one-piece balls, which are easy to construct and relatively inexpensive, but have poor playing characteristics and are thus generally limited for use as range balls. Two-piece balls are constructed with a generally solid core and a cover and are generally the most popular with recreational golfers because they are very durable and provide maximum distance. Balls having a two-piece construction are commonly formed of a polymeric core encased by a cover. Typically, the core is formed from polybutadiene that is chemically crosslinked with zinc diacrylate and/or other similar crosslinking agents. These balls are generally easy to manufacture, but are regarded as having limited playing characteristics. Solid golf balls also include multi-layer golf balls that are comprised of a solid core of one or more layers and/or a cover of one or more layers. These balls are regarded as having an extended range of playing characteristics.
Wound golf balls are generally preferred by many players due to their high spin and soft xe2x80x9cfeelxe2x80x9d characteristics. Wound golf balls typically include a solid, hollow, or fluid-filled center, surrounded by a tensioned elastomeric material and a cover. Wound balls generally are more difficult and expensive to manufacture than solid two-piece balls.
Golf ball performance characteristics are typically described in terms of their distance, durability, spin and feel. These characteristics need not be mutually exclusive, and yet golf balls that have a suitable feel, such as those with balata covers, tend not to be extraordinarily durable. This is because materials that have high tensile and compressive strengths often diminish the compressibility of the balls into which they are incorporated, and thus they generally feel hard. There thus exists a need for resilient and durable materials that may be used to form golf ball covers, mantle layers, and centers that retain the soft feel desired by many golfers.
Numerous attempts have been made to provide such materials. For example, U.S. Pat. Nos. 4,274,637 and 4,431,193 disclose covers and mantle layers, respectively, made of cellular, or foamed ionomer materials. These materials, which are lighter than the solid materials from which they are made, are produced with blowing agents, nucleating agents, and other additives that thermally decompose at high temperatures to form bubbles within a polymer melt. Foamed materials made in this manner are hereinafter referred to as xe2x80x9cconventional foams.xe2x80x9d
U.S. Pat. No. 5,824,746 discloses golf balls covers comprising foamed, metallocene-catalyzed polymers. These polymers were also formed using conventional blowing or foaming agents.
The use of foamed materials can alter the coefficient of restitution of a golf ball, which is generally indicative of its resiliency. Resiliency, which is regulated by the U.S. Golf Association, is measured by the xe2x80x9cInitial Velocity Test,xe2x80x9d wherein a golf ball is struck by a club face moving at a speed of approximately 146 feet per second. Once struck by the club face, the velocity of the ball is measured. The maximum prescribed limit for a golf ball tested in this manner is 250+2% ft/s at 75xc2x0 F.
Conventional foams typically include about 103 to 106 cells/cm3, with the cells averaging about 100 xcexcM or larger in diameter. It is this large average size and an uneven cell size distribution that are believed to account for the relatively poor mechanical properties of conventional foams. See, e.g., Behravesh, A. H., et al., Antec ""98 Conference Proceedings, vol. II, pp. 1958-1967 (Apr. 26-30, 1998). Consequently, golf balls including conventional foams are expected to be inferior compared to those that do not include such conventional foams.
A further limitation of conventional foams is that they cannot be used to form materials thinner than the average cell size of about 100 xcexcM. This limitation restricts the applications in which foamed materials may be used. In addition, the conventional foams require chemical blowing agents, which may produce some environmental concerns.
A material property of conventional foams can be modified or improved by the use of microcellular materials. These materials are made by exposing a polymer melt to a gas under high pressure, and then quickly removing that pressure. The resulting cells are smaller, more narrowly distributed with regard to size, and occur in higher densities than those of conventional foams. Until recently, however, microcellular materials were made primarily from simple, single component polymer melts, such as polystyrene.
For example, U.S. Pat. No. 4,473,665 discloses microcellular closed cell foams made from polystyrene, polycarbonate, polyester, nylon, or a thermoplastic material, and a method of making such foams. Also disclosed are closed cell sizes on the order of 2 to 25 microns, as well as the addition of fillers such as carbon black to control void size.
U.S. Pat. No. 5,160,674 discloses microcellular foams of amorphous or semi-crystalline polymers, such as polyethylene or polypropylene, having bubbles on the order of 5 to 25 microns in diameter with bubble density of approximately 1010 bubbles/cm3.
Recently, reports have begun to surface in the literature of microcellular materials made from mixtures of polymeric and other compounds such as cellulose fiber. See, e.g., Barlow, C., et al., Antec ""98 Conference Proceedings vol. II, pp. 1944-1948 (Apr. 26-30, 1998); and Matuana, L. M. et al., Antec ""98 Conference Proceedings vol. 11, pp. 1968-1975 (Apr. 26-30, 1998).
U.S. Pat. No. 5,181,717 discloses an inflated bladder-type sports or leisure ball, e.g., a football, that includes an external layer of polyurethane or polyurethane-polyurea foam with compact integral skin. The foamed layer is microalveolate or microcellular at its core, with a compact skin and an intermediate zone between the core and skin with progressively smaller cells towards the skin.
WO 99/63019 discloses microcellular thermoplastic elastomeric polymeric structures having an average cell size less than 100 xcexcm in diameter. These materials may be formed from a thermoplastic elastomeric olefin, preferably metallocene-catalyzed polyethylene, with article densities ranging from less than 0.5 g/cm3 to less than 0.3 gm/cm3.
U.S. Pat. No. 6,037,383 discloses microcellular polyurethane elastomers having improved dynamic properties based on an isocyanate consisting essentially of 4,4""-MDI.
Despite these disclosures of microcellular materials, however, Applicants are not aware of any disclosures that include such microcellular materials in golf balls. Thus, the need still exists to produce components with material properties modified by the use of microcellular materials.
This invention is directed to microcellular golf ball-forming materials for one-piece, two-piece, and multi-layer (i.e., three or more layers) golf balls, such as golf balls that are fluid-filled, include one or more wound layers, include a multi-layer cover, and the like.
In particular, the invention encompasses a golf ball including at least one core layer and at least one cover layer disposed over the at least one core layer, with the at least one cover layer having a thickness of at least about 0.03 inches, wherein at least one of the core layers or cover layers is formed of a microcellular composition having an average cavity density of about 105 cavities/cm3 to 1014 cavities/cm3, and an average cavity diameter of less than about 100 microns. In one embodiment, the cover has at least one of a dimple coverage of greater than about 60 percent, a hardness from about 35 to 80 Shore D, or a flexural modulus of greater than about 500 psi, and the golf ball has at least one of a compression from about 50 to 120 or a coefficient of restitution of greater than about 0.7.
The microcellular composition preferably has an average cavity diameter from about 0.1 microns to 95 microns, more preferably from about 5 microns to 50 microns. The microcellular composition can further include at least one of a stabilizer, crosslinking agent, pigment, brightener, lubricant, or density-adjusting filler. In particular, the microcellular composition preferably includes a polymer selected from the group of thermoplastics, thermoplastic elastomers, rubbers, thermosets, and mixtures thereof.
In one embodiment, the microcellular composition includes a polymer having a hardness of at least about 15 Shore A, a flexural modulus of at least about 500 psi, a density of at least about 0.3 g/cm3, and a rebound of at least about 30%. In another embodiment, the polymer includes at least one of a copoly(ether-ester), copoly(ether-urethane), copoly(ester-urethane), copoly(ether-amide), or metallocene-catalyzed polymer.
As noted above, any type of golf ball construction may be formed according to the invention. In one embodiment, at least one of the core layers includes the microcellular composition. In another embodiment, the core layers include at least one center layer including a fluid and at least one intermediate layer including the microcellular composition disposed about the at least one center layer. In yet another embodiment, the golf ball has at least two core layers including a first core layer including a tensioned elastomeric material wound about a second core layer including the microcellular composition. The microcellular composition can be included to modify the density and/or moment of inertia of the golf ball or portions thereof. The moment of inertia of the golf ball should typically be from about 0.3 to 0.9 g/cm2.
The invention also relates to a golf ball having an Atti compression of at least about 50 and a coefficient of restitution of at least about 0.7 at 125 ft/sec that includes a solid core having a deflection of about 1 mm to 6 mm under a load of 100 kg, and at least one cover layer disposed over the core and being formed of a microcellular composition having an average cavity density of about 105 cavities/cm3 to 1014 cavities/cm3, and an average cavity diameter of less than about 100 microns.
The invention also encompasses a golf ball having an Atti compression of at least about 50 and a coefficient of restitution of at least about 0.7 at 125 ft/sec that includes a core, an inner cover layer disposed over the core and being formed of a microcellular composition having an average cavity density of about 105 cavities/cm3 to 1014 cavities/cm3, and an average cavity diameter of less than about 100 microns, and an outer cover layer disposed over the inner cover layer and having a flexural modulus of about 10,000 psi to 70,000 psi.
Methods of forming such golf balls are also encompasses by the invention. In one embodiment, a method of adjusting at least one material property or weight distribution of a golf ball includes at least partially melting a polymeric material, saturating the melted polymeric material with a gas at a first pressure sufficient to substantially uniformly distribute the gas through the melted polymeric material, shaping the gas-saturated polymeric material at an elevated pressure to prevent substantial cell nucleation within the material, sufficiently reducing the first pressure, in the absence of sonic vibration, and supersaturating the shaped polymer material with a gas so that the polymer material is modified to form a substantially uniformly nucleated shaped microcellular polymeric material having closed-cell, microcellular voids having a diameter of no greater than about 100 microns, solidifying the microcellular polymer material sufficiently to inhibit formation of additional voids, and incorporating the microcellular polymeric material into a golf ball.
The polymeric material is preferably selected from the group of thermoplastics, thermoplastic elastomers, rubbers, thermosets, and mixtures thereof. In a preferred embodiment, the polymeric material is combined with at least one additive before being exposed to the gas. The at least one additive typically includes a stabilizer, crosslinking agent, pigment, brightener, lubricant, density-adjusting filler, or a combination thereof.
The method preferably uses a gas that includes air, a noble gas, nitrogen, carbon dioxide, or a mixture thereof. The gas flow rate is typically at least about 0.005 lbs./hr.
The incorporating into a golf ball can include forming the microcellular composition into portion of a golf ball core, and disposing a dimpled outer cover over the core so as to form the golf ball. In one embodiment, the forming includes forming the microcellular composition into a golf ball center, and providing at least one mantle layer over the center. In the alternative, the incorporating step can include forming a golf ball core, and forming a material including the microcellular composition into at least a portion of a golf ball cover. In another embodiment, the forming includes at least one of injection molding, compression molding, reaction injection molding, or casting the microcellular composition. In yet another alternative, the golf ball can be a one-piece golf ball formed of a material including the microcellular composition.
This invention is also directed to a method of affecting the weight distribution within a golf ball. In this embodiment, the moment of inertia may be adjusted by varying the type and density of the microcellular materials of the invention. For example, a golf ball can be prepared having a moment of inertia from about 0.3 g/cm2 to 0.9 g/cm2. In another embodiment, this invention encompasses a method of modifying the material properties of the golf ball components. This method includes the incorporation of a microcellular material into a golf ball as described herein.